The right supplements can help your heart, sharpen your immune system, and even improve your sex life. The wrong ones, however, can be ineffective or even harmful. “You run into problems because most men are ‘prescribing’ these things themselves,” says Tod Cooperman, M.D., president of consumerlab.com, an independent tester of health and nutritional products. “Don’t take supplements with abandon. They should be used carefully, because taking in too much of certain nutrients can cause problems.”

We consulted with top doctors, reviewed the latest research, and waded through marketers’ claims to bring you 18 of the best supplements for men. Use our guide—along with advice from your own doc, since many supplements can interact with other medications—to fine-tune your strategy.

ACETYL L-CARNITINE

Problem: Brain drain

This amino acid converts fats to energy and boosts antioxidant activity in the body. In supplement form, it may protect gray matter from stress caused by alcohol and aging. And in a 2006 study, people who received 1,000 milligrams (mg) of acetyl L-carnitine a day saw relief from mild chronic depression.

Dose: 1,000 mg/day
Our pick: Vitamin World Acetyl L-Carnitine, 1,000 mg; vitaminworld.com ($50/60 capsules)

Natural sources: Red meat, dairy products

KOREAN RED PANAX GINSENG

Problem: Erectile dysfunction

Sixty percent of men with erectile dysfunction who took this supplement noticed improvement, according to a 2002 Korean study. The herb may also protect your heart—in a recent Canadian study, a daily dose reduced arterial stiffness.

Dose: 900 mg, up to three times a day
Our pick: Vitamin World Korean Ginseng, 500 mg; vitaminworld.com ($13/100 capsules)

Natural sources: Korean ginseng root

COENZYME Q-10

Problem: High blood pressure

CoQ-10 can lower your blood pressure while boosting your levels of ecSOD, an enzyme thought to protect blood vessels from damage. CoQ-10 may also improve sperm quality, Italian researchers say. Japanese researchers found it can increase fat burning during exercise.

Dose: 30 to 200 mg/day
Our pick: Carlson Co-Q10, 100 mg; carlsonlabs.com ($40/90 soft gels)

Natural sources: Meat and fish, eggs, broccoli