Perindopril, is an anti hypertensive medicine that can cause erectile dysfunction as a side effect.
His sexual dysfunction can be due to his hypertension, too.
Acctually, having a high blood pressure for years is linked with blood vessels narrowing, that is a direct cause of erectile dysfunction.
He can talk with his physician to get switched to another antihypertensive drug (another class) that have less negative impact on sexual function (some studies have shown that Loresta, a type of antihypertensive drug can even make male sexual function better).
It is far more important to have regulated blood pressure on daily basis.
Some patients, report increased frequency of attacks of sinusitis and post nasal drip (phlegm in his throat) while being on Perindopril.
Another side effect is being nauseous (nausea can be due to phlegm, too).
The accumulation of phlegm and swallowing it repeatedly can lead to vomiting.
It is important to pay attention to attacks of vomiting, cause they may indicate severe going up of hypertension (increasing).

Best wishes!
Marija