My boyfriend used to do drugs like meth and cocaine what effects would that have on his fertility? He's been clean for 4yrs but still smokes cigarettes

Should be ok. Drugs like meth and Cocaine can cause issues with infertility, most most commonly when using. Severe chronic abuse can cause damage, but at his age he should be fine now that he stopped. Smoking should not be an issue, but he should eventually work on that too and stop. Best wishes.
Men's health . Probably nothing now. If he is truly sober and not on any anabolic or other hormonal supplements he is probably just as fertile as the next guy.