Timolol

What it is

Timolol maleate is a synthetic drug that blocks both beta1 and beta2 adrenergic receptors without the partial agonist or membrane-stabilising activity some other beta blockers have. It is sold as eye drops (0.25% and 0.5% solutions and gel-forming solutions, alone or combined with dorzolamide or brimonidine) for raised eye pressure, and as oral tablets for high blood pressure, for secondary prevention after a heart attack and for migraine prevention. Eye drops are not confined to the eye: a large fraction of the dose reaches the bloodstream and avoids first-pass liver metabolism.

What the research says

For the eye, the evidence is strongest for what timolol measurably does - it lowers intraocular pressure - and much weaker for the outcome people care about, preserved sight. A Cochrane review found that IOP-lowering medicines as a class reduce new visual field defects in ocular hypertension, but that no single drug, timolol included, showed a significant visual field benefit on its own. After a heart attack the evidence is a genuine mortality benefit from a large placebo-controlled trial. For ordinary high blood pressure, beta blockers as first-line treatment come out worse than other drug classes. For migraine prevention the supporting trial is one small crossover study from 1984.

Evidence grade: Disputed.

How it works

Drug class: Non-selective beta-adrenergic receptor blocking agent (beta blocker), supplied as eye drops and as oral tablets

Timolol blocks beta1 and beta2 adrenergic receptors, the docking points for adrenaline and noradrenaline. In the heart this slows the rate and reduces output; in the airways it increases resistance, which is why it is dangerous in asthma. In the eye it lowers pressure, and tonography and fluorophotometry studies suggest this is mainly because the eye makes less aqueous fluid rather than drains more. (Source 1)

What it is used for

• Timolol drops reliably lower eye pressure. Pressure-lowering treatment as a class reduces the onset of visual field defects in ocular hypertension (OR 0.62), but the Cochrane review found no single drug, including timolol, showed a significant visual field benefit by itself, and a USPSTF evidence review found treatment lowered progression (absolute risk difference -4.2%) while one trial found no difference in visual acuity, quality of life or function. Evidence: limited. (Source 2)
• In the Norwegian Multicenter Study, 1,884 survivors of myocardial infarction were randomised to timolol 10 mg twice daily or placebo: 152 deaths on placebo versus 98 on timolol, sudden death 13.9% versus 7.7% over 33 months, reinfarction 20.1% versus 14.4%. A separation in mortality was still present at six years. Evidence: established. (Source 3)
• The Cochrane review of beta blockers as first-line treatment for hypertension found no difference in all-cause mortality against placebo and no difference in coronary heart disease, with a reduction in total cardiovascular disease driven by stroke; the reviewers concluded beta-blocker effects are inferior to those of other antihypertensive drugs, and that most of the trials carry a high risk of bias. Three-quarters of the participants took atenolol rather than timolol. Evidence: disputed. (Source 4)
• The approval rests largely on a 1984 double-blind crossover study in 107 patients: global response 65% on timolol versus 40% on placebo, but the severity and duration of the headaches that still occurred were unchanged. This is one small trial, not a literature. Evidence: limited. (Source 5)
• A meta-analysis of 11 randomised trials (1,235 patients) found topical beta blockers more effective than placebo, corticosteroids or pulsed dye laser for superficial infantile haemangioma (RR 2.25, 95% CI 1.66-3.05) and about as effective as oral propranolol, with fewer adverse effects than oral propranolol. An earlier systematic review of 31 studies found a large pooled response rate but graded the quality of evidence low to moderate and called for adequately powered trials. Evidence: limited. (Source 6)

Interactions

• Quinidine and other CYP2D6 inhibitors (including the SSRIs paroxetine and fluoxetine) (pharmacokinetic study): Timolol is cleared by the liver enzyme CYP2D6. Blocking that enzyme raises blood levels of timolol even when it was only put in the eye, and deepens the slowing of the heart. (Source 7)
• Verapamil, diltiazem and other calcium channel blockers (label): Taken with a beta blocker these can disturb electrical conduction between the upper and lower chambers of the heart, weaken the left ventricle and drop blood pressure. (Source 8)
• Oral beta blockers and a second topical beta blocker (label): The beta-blocking effects add up, on the heart as well as on eye pressure; the label advises against using two beta-blocker eye drops together. (Source 9)
• Reserpine and other catecholamine-depleting drugs (label): Added together with a beta blocker these can cause low blood pressure or a markedly slow pulse, with dizziness, fainting or light-headedness on standing. (Source 8)
• Clonidine withdrawal (label): Oral beta blockers can worsen the blood-pressure rebound that follows stopping clonidine. The label records no reports of this with timolol eye drops. (Source 10)

Stopping it

• Beta blockers should not be stopped abruptly. The oral timolol label records hypersensitivity to catecholamines after withdrawal, with worsening angina and in some cases myocardial infarction after abrupt discontinuation. (Source 11)
• The label's stated taper, as a position dated 2022, is a gradual reduction over one to two weeks with careful monitoring, and it suggests not stopping abruptly even when timolol was given only for blood pressure. (Source 11)
• Where coronary disease may be present but unrecognised, the label advises against abrupt discontinuation even in people treated only for hypertension. (Source 11)

What goes wrong

Ophthalmic timolol is absorbed systemically in large amounts and can cause serious cardiac adverse effects including bradycardia, conduction disorders, syncope and falls. (Source 12)

• Expert review, not systematic, Low certainty.
• Size: not stated (expert review)
• Who: Patients using timolol eye drops for glaucoma.
• How long: not applicable.
• Result: About 80% of the drug in the ophthalmic products is reported to be systemically absorbed with first-pass metabolism avoided; named harms include symptomatic bradycardia, conduction disorders, orthostatic hypotension, syncope and falls.
• Funding: not stated.

Limit of this finding: This is a narrative expert-opinion review, not a study, so nothing in it is a new measurement. In particular the figure that about 80% of the drug in ophthalmic products is systemically absorbed is an assertion the authors make in their abstract without citing a source for it, and should be read as expert opinion rather than as a measured value. The adverse effects it lists are real and appear on the product label; the absorption percentage is the part to treat cautiously.

Ophthalmic timolol may cause serious adverse effects such as symptomatic bradycardia, various conduction disorders in the heart, orthostatic hypotension, syncope and falls.

People taking a beta blocker for hypertension stopped treatment for adverse events more often than people taking a renin-angiotensin system inhibitor. (Source 4)

• Systematic review, Moderate certainty.
• Size: 3 RCTs, 10,828 participants in the RAS inhibitor comparison.
• Who: Adults with hypertension.
• How long: trials of at least one year.
• Result: Discontinuation due to adverse events RR 1.41, 95% CI 1.29 to 1.54.
• Funding: not stated.

Limit of this finding: Two cautions. The review describes all-cause mortality as higher on beta blockers than on calcium-channel blockers while reporting RR 1.07 with a 95% confidence interval of 1.00 to 1.14 - an interval whose lower limit is exactly no difference - so that particular comparison is not established by its own numbers. And the review states that most of its thirteen trials, run between the 1970s and the 2000s, had a high risk of bias, and that three-quarters of the 40,245 people taking a beta blocker were taking atenolol, so these figures mainly describe one older drug.

Participants taking beta-blockers were more likely to discontinue treatment due to adverse events than participants taking RAS inhibitors (RR 1.41, 95% CI 1.29 to 1.54; moderate-certainty evidence)

Timolol eye drops lowered exercise heart rate, and the drop was larger in people who cannot metabolise the drug via CYP2D6. (Source 7)

• Blood level study, Low certainty.
• Size: 13 men (8 extensive metabolisers, 5 poor metabolisers of debrisoquin)
• Who: Healthy male volunteers at an academic clinical research centre.
• How long: single-dose crossover.
• Result: Exercise heart rate reduced versus placebo in both groups (P < .001); greater reduction (P = .01) and higher plasma timolol (P = .03) in poor metabolisers.
• Funding: not stated.

The exercise heart rate was reduced following timolol eye drops compared with placebo in both EMs (P < .001) and PMs (P < .001) with significantly greater heart rate reduction (P = .01) and higher plasma timolol concentration in PMs compared with EMs (P = .03).

The FDA label for timolol eye drops records deaths from bronchospasm in people with asthma and, rarely, deaths associated with cardiac failure after ophthalmic as well as systemic use - a regulator's position dated 2026. (Source 13)

• Official position, Certainty not rated.
• Size: not stated.
• Who: Patients given topical or systemic timolol maleate.
• How long: not applicable.
• Result: No rate given; the label states the events have been reported following systemic or ophthalmic administration.
• Funding: manufacturer label.

For example, severe respiratory reactions and cardiac reactions, including death due to bronchospasm in patients with asthma, and rarely death in association with cardiac failure, have been reported following systemic or ophthalmic administration of timolol maleate USP

The commonest adverse experience with timolol eye drops on the label is burning and stinging on instillation, in roughly one in eight patients - a label position dated 2026. (Source 14)

• Official position, Certainty not rated.
• Size: not stated.
• Who: Patients using timolol maleate ophthalmic solution.
• How long: not applicable.
• Result: Burning and stinging upon instillation in approximately one in eight patients.
• Funding: manufacturer label.

The most frequently reported adverse experiences have been burning and stinging upon instillation (approximately one in eight patients).

The only randomised trial of glaucoma screening itself found no vision benefit and a significantly greater risk of falls in the people screened. (Source 15)

• Systematic review, Low certainty.
• Size: 1 randomised trial, 616 frail elderly participants, within a review of 83 studies and 75,887 people.
• Who: Frail elderly persons offered glaucoma screening versus no screening.
• How long: Not stated in the abstract.
• Result: No difference in vision outcomes versus no screening, but significantly greater falls risk, relative risk 1.31 (95% CI 1.13-1.50)
• Funding: Agency for Healthcare Research and Quality review for the US Preventive Services Task Force.

Limit of this finding: This is the harm of the screening programme, not of timolol. It matters here because pressure-lowering eye drops such as timolol are what screening leads to, and the same review found the treatment benefit was measured on eye-pressure and progression scales rather than on vision, quality of life or function.

One RCT (n = 616) found screening of frail elderly persons associated with no difference in vision outcomes vs no screening but with significantly greater falls risk (relative risk [RR], 1.31 [95% CI, 1.13-1.50]).

What the evidence supports

In survivors of acute myocardial infarction, timolol 10 mg twice daily reduced deaths, sudden death and reinfarction compared with placebo. (Source 3)

• Randomized trial, High certainty.
• Size: 1,884 patients (945 timolol, 939 placebo)
• Who: Patients surviving acute myocardial infarction, treatment started 7 to 28 days after infarction.
• How long: 12 to 33 months (mean 17)
• Result: 152 deaths on placebo versus 98 on timolol; cumulated sudden-death rate 13.9% placebo versus 7.7% timolol (P = 0.0001); cumulated reinfarction 20.1% versus 14.4% (P = 0.0006)
• Funding: not stated.

the cumulated sudden-death rate over 33 months was 13.9 per cent in the placebo group and 7.7 per cent in the timolol group--a reduction of 44.6 per cent (P = 0.0001)

The mortality separation between timolol and placebo after myocardial infarction persisted to six years. (Source 16)

• Randomized trial, Moderate certainty.
• Size: 1,884 patients randomised.
• Who: Survivors of acute myocardial infarction.
• How long: up to 72 months after randomisation.
• Result: Cumulated mortality 32.3% placebo versus 26.4% timolol (P = 0.0028)
• Funding: not stated.

Cumulated mortality rates were 32.3 per cent in the placebo group and 26.4 per cent in the timolol group (P = 0.0028).

Pressure-lowering drug treatment as a class reduced the onset of visual field defects in ocular hypertension. (Source 17)

• Systematic review, Moderate certainty.
• Size: 26 trials, 4,979 participants randomised (10 trials in the visual field meta-analysis)
• Who: Adults with primary open angle glaucoma or ocular hypertension.
• How long: at least one year of treatment per trial.
• Result: OR 0.62, 95% CI 0.47 to 0.81 for onset of visual field defects in treated ocular hypertension; for beta blockers specifically OR 0.67, 95% CI 0.45 to 1.00.
• Funding: not stated.

Limit of this finding: The review contradicts itself about beta blockers. Its results say no single drug showed a significant visual-field protective effect and give the beta-blocker estimate as OR 0.67 with a 95% confidence interval of 0.45 to 1.00, an interval that reaches exactly no effect; its conclusions then say positive evidence for beta blockers 'has been shown'. The class-wide pressure-lowering result (OR 0.62, 0.47 to 0.81) is the statistically significant one; the beta-blocker-specific estimate is not. This version also searched only to May 2007.

Meta-analysis of 10 trials clearly demonstrated reduction of onset of VF defects in treated OHT (OR 0.62, 95% CI 0.47 to 0.81).

Topical beta blockers, timolol among them, outperformed placebo, corticosteroids or pulsed dye laser for superficial infantile haemangioma and matched oral propranolol. (Source 6)

• Meta-analysis, Low certainty.
• Size: 11 randomised controlled trials, 1,235 patients.
• Who: Infants with superficial or mixed infantile haemangioma.
• How long: not stated in the abstract.
• Result: Versus placebo, corticosteroids or pulsed dye laser RR 2.25, 95% CI 1.66-3.05, p < 0.00001; versus oral propranolol RR 0.96, 95% CI 0.91-1.02, p = 0.20.
• Funding: not stated.

blockers were more beneficial than placebo, corticosteroids or pulsed dye laser in treating SIH (RR 2.25, 95% CI 1.66-3.05, p < 0.00001, I2 = 0%)

What the evidence does not support

No single glaucoma drug, timolol included, showed a significant visual field protective effect against placebo or no treatment. (Source 17)

• Systematic review, Moderate certainty.
• Size: 26 trials, 4,979 participants.
• Who: Adults with primary open angle glaucoma or ocular hypertension.
• How long: trials of at least one year.
• Result: No single drug significant versus placebo or untreated controls; beta blockers only borderline (OR 0.67, 95% CI 0.45 to 1.00)
• Funding: not stated.

Limit of this finding: The review contradicts itself about beta blockers. Its results say no single drug showed a significant visual-field protective effect and give the beta-blocker estimate as OR 0.67 with a 95% confidence interval of 0.45 to 1.00, an interval that reaches exactly no effect; its conclusions then say positive evidence for beta blockers 'has been shown'. The class-wide pressure-lowering result (OR 0.62, 0.47 to 0.81) is the statistically significant one; the beta-blocker-specific estimate is not. This version also searched only to May 2007.

No single drug showed a significant VF protection compared to placebo or untreated controls.

Lowering eye pressure with medicine reduced measured glaucoma progression but did not translate into better vision, quality of life or function in the one trial that measured those. (Source 15)

• Systematic review, Moderate certainty.
• Size: 7 trials, 3,771 participants for the treatment comparison; 1 trial, 461 participants for functional outcomes.
• Who: Adults with ocular hypertension or untreated glaucoma.
• How long: not stated in the abstract.
• Result: RR 0.68 (95% CI 0.49-0.96) for progression, absolute risk difference -4.2% versus placebo; no differences in visual acuity, quality of life or function in the single trial reporting them.
• Funding: Agency for Healthcare Research and Quality review for the USPSTF.

Medical therapy for ocular hypertension and untreated glaucoma was significantly associated with decreased intraocular pressure and decreased likelihood of glaucoma progression (7 trials, n = 3771; RR, 0.68 [95% CI, 0.49-0.96]; absolute risk difference -4.2%) vs placebo, but 1 trial (n = 461) found no differences in visual acuity, quality of life, or function.

As first-line treatment for high blood pressure, beta blockers showed no mortality benefit over placebo and no reduction in coronary heart disease. (Source 4)

• Systematic review, Moderate certainty.
• Size: 13 RCTs; 23,613 participants in the placebo comparison; 40,245 participants taking beta blockers in total.
• Who: Adults with hypertension and no compelling indication for a beta blocker.
• How long: trials of at least one year.
• Result: All-cause mortality RR 0.99, 95% CI 0.88 to 1.11 versus placebo; coronary heart disease RR 0.93, 95% CI 0.81 to 1.07.
• Funding: not stated.

Limit of this finding: Two cautions. The review describes all-cause mortality as higher on beta blockers than on calcium-channel blockers while reporting RR 1.07 with a 95% confidence interval of 1.00 to 1.14 - an interval whose lower limit is exactly no difference - so that particular comparison is not established by its own numbers. And the review states that most of its thirteen trials, run between the 1970s and the 2000s, had a high risk of bias, and that three-quarters of the 40,245 people taking a beta blocker were taking atenolol, so these figures mainly describe one older drug.

There was no difference in all-cause mortality between beta-blockers and placebo (RR 0.99, 95% CI 0.88 to 1.11)

The Cochrane reviewers judged beta-blocker effects in hypertension inferior to other antihypertensive classes and the underlying trials at high risk of bias. (Source 18)

• Systematic review, Moderate certainty.
• Size: 13 RCTs.
• Who: Adults with hypertension.
• How long: trials of at least one year.
• Result: Authors' conclusion of modest cardiovascular disease reduction, little or no mortality effect, and inferiority to other classes; most trials at high risk of bias; atenolol was the beta blocker most used.
• Funding: not stated.

Current evidence suggests that initiating treatment of hypertension with beta-blockers leads to modest CVD reductions and little or no effects on mortality. These beta-blocker effects are inferior to those of other antihypertensive drugs.

Adding a topical beta blocker to another treatment for mixed infantile haemangioma gave no safety advantage: adverse effects were no different from the comparison treatment. (Source 6)

• Meta-analysis, Low certainty.
• Size: 1,235 patients across 11 randomised controlled trials, 5 of them in mixed infantile haemangioma.
• Who: Infants with superficial or mixed infantile haemangioma.
• How long: Not stated in the abstract.
• Result: RR 1.01, 95% CI 0.58-1.74, p = 0.98, I2 = 0% for adverse effects when a topical beta blocker was combined with another intervention.
• Funding: not stated.

Limit of this finding: The favourable safety figure in this review (RR 0.05 against oral propranolol) applies only to using a topical beta blocker instead of the oral drug. Where the topical drug was added on top of another treatment, the same review found no safety difference at all. Do not read the 0.05 figure as applying to combination treatment.

No significant difference in adverse effects was found when a topical β-blocker was combined with another intervention in treating MIH (RR 1.01, 95% CI 0.58-1.74, p = 0.98, I2 = 0%).

Where the evidence is mixed

Timolol reduced migraine frequency and global response versus placebo but did not change the severity or duration of the headaches that still happened. (Source 5)

• Randomized trial, Low certainty.
• Size: 107 randomised, 94 completed.
• Who: Adults with frequent migraine headache (77 women, 30 men)
• How long: 20-week double-blind crossover.
• Result: Overall global response 65% with timolol versus 40% with placebo; severity and duration of headaches unchanged.
• Funding: not stated.

Limit of this finding: This 1984 crossover trial reports no confidence intervals and no p-values for its headline figures, and it gives no analysis of the 13 of 107 patients who did not finish, yet it concludes that timolol is a safe and effective treatment. The 65% versus 40% global-response difference is one small trial's unadjusted result, and the paper itself records that the severity and duration of the headaches that still occurred were unchanged.

Overall global response rates were 65% with timolol compared with 40% with placebo.

A systematic review of topical timolol for infantile haemangioma pooled a large improvement rate, but on low to moderate quality evidence and with no stated comparison group. (Source 19)

• Systematic review, Low certainty.
• Size: 31 studies, 691 patients.
• Who: Infants with infantile haemangioma treated with topical timolol.
• How long: Not stated in the abstract.
• Result: Fixed-effects pooled response rate, defined as any improvement from baseline, RR = 8.96 (95% CI 5.07-15.47), heterogeneity test p = 0.99.
• Funding: not stated.

Limit of this finding: Two problems with the number itself. The review reports a risk ratio of 8.96 without ever saying what the comparison group was, so the ratio has no stated comparator. And it reports a heterogeneity test of p = 0.99 across 31 studies, which would mean essentially no variation at all between 31 separate studies of a visible skin outcome; that is not credible and it makes the fixed-effects pooling the authors used inappropriate. The authors themselves rate the quality of the evidence as low to moderate and call for adequately powered randomised trials.

The fixed effects pooled estimate of the response rate defined as any improvement from baseline of infantile hemangioma after treatment with topical timolol was significant (RR = 8.96; 95% CI 5.07-15.47; heterogeneity test p = 0.99), and the treatment was overall well tolerated.

Where the research disagrees

Whether lowering eye pressure with timolol actually preserves sight, as opposed to lowering a number

• Cochrane review authors (Vass and colleagues, 2007), systematic review of 26 trials, 4,979 participants: Positive but weak evidence for a beneficial effect of the class of beta-blockers has been shown. (Source 17)
• USPSTF evidence review authors (Chou and colleagues, 2022), systematic review of 83 studies, 75,887 people: Screening tests can identify persons with glaucoma and treatment was associated with a lower risk of glaucoma progression, but evidence of improvement in visual outcomes, quality of life, and function remains lacking. (Source 20)

How much

• Reference intake: Dosing is set by the prescriber, not by the reader. As a position, the 2026 ophthalmic label states the usual starting dose is one drop of 0.25% solution in the affected eye or eyes twice a day; the 2022 oral label states the usual initial dose for hypertension is 10 mg twice a day with a usual maintenance of 20 to 40 mg per day. (Source 21)
• Upper limit: As a position, the 2022 oral label states increases to a maximum of 60 mg per day in two divided doses may be necessary for hypertension, and for migraine a maximum of 30 mg daily in divided doses; the 2026 ophthalmic label states doses above one drop of 0.5% twice a day generally have not been shown to lower intraocular pressure further. (Source 22)
• Studied: The Norwegian Multicenter Study gave timolol 10 mg twice daily to survivors of myocardial infarction. (Source 3)
• Studied: The 1984 migraine crossover study gave timolol maleate 20 to 30 mg/day. (Source 5)
• Studied: The CYP2D6 interaction study gave two drops of 0.5% timolol with or without 50 mg oral quinidine. (Source 23)

A common belief, and what the research shows

The belief: Eye drops stay in the eye, so a beta blocker given as drops cannot affect the heart or lungs.

What the research shows: The label itself opens its warnings with the opposite: As with many topically applied ophthalmic drugs, this drug is absorbed systemically. A pharmacology review puts the systemically absorbed fraction at about 80% with first-pass metabolism bypassed, and reports bradycardia, conduction disorders, syncope and falls.

Questions and answers

What is it?

Timolol maleate is a beta blocker: it blocks both beta1 and beta2 adrenergic receptors, the docking points for adrenaline. It has no partial stimulating activity and no local anaesthetic effect. It comes as eye drops for raised eye pressure and as tablets for blood pressure, after a heart attack, and for migraine prevention. (Source 24)

What does it do in the body?

In the eye it lowers pressure, and tonography and fluorophotometry studies in people suggest this is mainly because the eye produces less aqueous fluid. Elsewhere in the body the same receptor blockade slows the heart and reduces its output, and increases airway resistance in the lungs, which is why it is dangerous in asthma. (Source 1)

Is it good or bad for you?

It depends entirely on the setting. After a heart attack a placebo-controlled trial showed fewer deaths and fewer reinfarctions. For ordinary high blood pressure, the Cochrane review found no mortality benefit over placebo and judged beta blockers inferior to other classes. For glaucoma, the drops reliably lower pressure, but the systematic reviews found the evidence that this preserves vision, quality of life and function is still lacking. (Source 20)

How do you get more of it?

Does not apply in the way it would for a nutrient. Timolol is a prescription medicine; there is no food or supplement that supplies it, and the amount a person gets is whatever the prescriber directs. The label's stated starting dose is one drop of the 0.25% solution in the affected eye or eyes twice a day, adjusted on the basis of measured eye pressure rather than on how the person feels. (Source 21)

If it is harmful, what reduces it?

Timolol clears from the body on its own once it is stopped, but it should not be stopped suddenly. The oral label describes exacerbation of angina and, in some cases, myocardial infarction after abrupt discontinuation, and sets out a gradual reduction over one to two weeks with monitoring. For an overdose or an unwanted systemic effect, the eye-drop label notes that beta blockade can be reversed with adequate doses of adrenergic agonists during surgery. (Source 11)

Why might someone be low in it or missing it?

Someone can be getting less effect than expected from the same dose because of how fast they break the drug down. Timolol is metabolised by CYP2D6, and in a crossover study people who metabolise the enzyme's substrates extensively had lower plasma timolol and less heart-rate slowing than poor metabolisers given the same drops. Blocking the enzyme, with quinidine for instance, pushed levels and effect up again. (Source 7)

Which whole foods contain it or feed it?

No whole food contains timolol and we found no food or beverage interaction documented for it in the sources we searched. The reason food matters less than it would for an oral drug is that eye drops reach the bloodstream directly: a pharmacology review reports about 80% of the drug in ophthalmic products is systemically absorbed and first-pass metabolism is avoided. (Source 12)

We searched: PubMed searches for timolol with food, grapefruit, supplement and alcohol interactions, plus the drug-interaction sections of the 2026 ophthalmic and 2022 oral DailyMed labels, which list only drug interactions

What happens if you do not have it?

Not taking timolol is not a deficiency; the question is what the untreated condition does. Raised eye pressure is a major risk factor for glaucomatous visual field loss, and the higher the pressure the greater the likelihood of field loss and optic nerve damage. After a heart attack, the placebo arm of the Norwegian trial had 152 deaths against 98 on timolol over a mean 17 months. (Source 1)

How can you test for it?

There is no routine blood test for timolol in ordinary care. What is measured instead is the thing it acts on: intraocular pressure by tonometry, plus heart rate and blood pressure for systemic effects. Tonometry on its own is a weak test for detecting glaucoma - the USPSTF evidence review pooled 13 studies in 32,892 people and found sensitivity of only 0.48 - so imaging and visual field testing are used alongside it. (Source 15)

References

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