Will smoking dope make me thick?

Yes, despite what potheads claim. Doctors in Greece compared the mental abilities of 20 people who had smoked dope four times a week for 15 years with 20 who had used it for less than seven years, and 24 never-smokers. They were given 15 words to learn, and asked to repeat them later. The average score for the long-term smokers was 7; for the shorter-term smokers, 9; for the never-users, 12. It is the latest in many studies showing repeated 'soft' drug abuse damages the brain. This isn't surprising because marijuana's active ingredient, tetrahydro cannabinol (THC), is highly fat-soluble. As our brain is the organ with the highest concentration of fat, THC makes a beeline for it and stays there for weeks.

Why is it that my laser eye surgeon wears glasses - does he know something I don't?

Yes, he does. He knows up to 5% of people who have laser surgery have permanently blurred vision afterwards that isn't fully corrected by glasses. There are two essential requirements of an eye surgeon: that he is good at his job and can see perfectly . Most people can, and do, get away with slightly impaired vision . But surgeons can't. I'd be lost without my glasses, but with them I can see well enough to watch a small white ball fly 200 yards from my club deep into gorse. As long as I can do that with my specs, I don't want laser surgery.

· Dr Tom Smith's Doctor, Have You Got A Minute? is published by Shortbooks at £9.99. Do you have a question for Dr Smith? Email doctordoctor@theguardian.com