Long-term use of erectile dysfunction drugs linked to higher glaucoma risk, study finds

Men who use a Viagra-like erectile dysfunction drug long-term are "significantly more likely" to develop glaucoma than those who do not, according to a new study.

The research, published in the British Journal of Ophthalmology, followed 74,000 men aged 40 years and older, half of whom had been prescribed tadalafil (sold under the brand names such as Cialis) over a period of five years.

Along with its use to treat erectile dysfunction, the drug is also used for the long-term treatment of urinary tract problems such as increased urgency associated with an enlarged prostate.

The researchers found people who used the drug long-term were 22 per cent more likely to develop glaucoma — a common eye disease which often leads to blindness — than those who did not.

"This is the first cohort study to show there is a correlation between taking these medications and an increased risk of developing glaucoma," said Flora Hui, an optometrist and research fellow at the Centre for Eye Research Australia, who did not contribute to the study.

Dr Hui said while the study showed the risk of having glaucoma was "statistically higher" in those who took the drug, the overall risk was still "quite low".

But, she said, it highlighted the importance of getting eyes tested before, and during the time of taking these medications, especially if a person had glaucoma risk factors.

"If you're a bit older, especially if you have a family history of glaucoma … and if you're going to be on long-term therapy, you really need to have regular eye tests because glaucoma can be largely symptomless."

PDE5i drugs and eye health

Tadalafil is part of a class of drugs called phosphodiesterase type 5 inhibitors (PDE5i), a group which also includes sildenafil (sold under the brand name Viagra).

Previous studies have linked PDE5i drugs with ophthalmological side effects, including those that affect the optic nerve, but until now, there has not been any research showing a strong link between a person taking tadalafil long-term and then developing glaucoma.

PDE5i inhibitors block a protein called PDE-5, increasing blood flow to the penis and helping people develop and maintain an erection.

They also relax muscle tissue and improve blood flow in organs such as the prostate and bladder.

While scientists still do not know exactly how these drugs increased a person's risk of developing glaucoma, Dr Hui said there were a few working theories.

People had a finite amount of blood in their body, Dr Hui said, which meant it had to "pull the blood from somewhere" to encourage it to go elsewhere.

"If you're getting transient episodes where you don't get sufficient blood to the nerve, then that can increase the chance of injury to the nerve and then potentially increase your risk of developing glaucoma."

Although the study was observational and did not prove that taking tadalafil caused participants to develop glaucoma, Dr Hui said it showed a "clear correlation" between the two, and highlighted the need for more in-depth research.

Andrew White, a clinician scientist ophthalmologist at Westmead Hospital and Westmead Institute for Medical Research, who did not contribute to the study, added that not everyone who took these drugs experienced the same side effects, or had any side effects at all.

Dr White said while some people experienced a temporary increase in pressure in the eye, others experienced low blood pressure.

"One of the other things that we have known for quite a long time is that if your blood pressure is too low or your blood pressure control varies a lot, then your glaucoma can also get worse," he said.

And the more "pressure spikes" someone experienced, the more likely they were to either develop glaucoma or make it worse, Dr White said.

Study participants not 'healthy'

The study, led by researchers from Taiwan, used data from 73,854 men from an international health database called TriNetX, excluding anyone with a history of glaucoma.

Researchers matched 36,927 people who used tadalafil with 36,927 men who did not use any PDE5i drugs.

While the drug is used to treat erectile dysfunction, small doses can also be taken daily over the long term to treat urinary tract symptoms.

The study found those who were prescribed the drug for urinary tract symptoms were 22 per cent more likely to develop glaucoma; 32 per cent more likely to have ocular hypertension and 33 per cent more likely to start glaucoma treatment than those who did not take it.

"Tadalafil use for lower urinary tract symptoms was associated with a significant increase in the risk of glaucoma, ocular hypertension, primary open-angle glaucoma and initiation of glaucoma treatment in a large, multinational, real-world cohort," researchers concluded.

The study found the risk increased in men aged over 50.

The study itself had a number of key limitations, including that most of the participants were white, and therefore the findings may not apply to men of other ethnicities.

And they were not able to factor in changes in medication or the development of other underlying conditions, which could increase someone's risk of developing glaucoma.

And this was important, Dr Hui said, as other variables could affect someone's eye health.

"About 40 per cent of them have high blood pressure, about 40 per cent of them have high cholesterol. These people do have comorbidities.

"It's a bit inconclusive about whether the additional chronic conditions made a difference."

Eye health monitoring needed

Although the study found a link between long-term use of tadalafil and glaucoma, the researchers stressed men should not stop using the drug for treatment of urinary tract symptoms.

Instead, they said, it indicated the need to have regular eye checks.

Dr Hui agreed.

"It's sometimes not the first thing we think about when we're taking these medications, but it's really important to get tested before you're starting these medications and if you are currently on them to get regular eye checks as well," she said.

Professor White said good monitoring and early intervention could improve someone's outcomes.

"If there is a reason for you to be monitored more closely, your local optometrist is a great start," he said.

"And the sooner we can pick something up, the sooner we can get on with treatment."

Dr Hui added that, for many, taking erectile dysfunction drugs could greatly improve someone's quality of life.

So a discussion about the potential risks and benefits was something for each patient to weigh up with their doctor.