The testicles make the hormone testosterone. This hormone helps in the formation of male sexual characteristics and plays a major role in maintaining muscle mass and healthy bone density. Healthy testosterone levels also fuel a man’s sex drive and a positive mental outlook.

However, testosterone production starts to decline starting around age 30. A blood test can determine your testosterone level and whether you fall into a low, high, or normal range. You may want to consider testosterone therapy if your levels drop significantly.

Testosterone is available as an injection, a patch, a gel, a pellet placed under the skin, and a tablet placed in the cheek until it dissolves. This type of hormone replacement therapy was shown to have high cardiovascular risks in the past. Recent research suggests that it may be safer than understood previously.

In 2015, the U.S. Food and Drug Administration (FDA) updated its 2014 recommendations for testosterone. The FDA now advises that testosterone should be approved only for people who have low testosterone because of certain medication conditions.

Medical conditions such as disorders of the testicles or a problem with the pituitary gland may cause low testosterone levels in men. Lowered testosterone also occurs as a normal result of aging and doesn’t always mean that something is wrong with you.

In the past, doctors frequently prescribed testosterone therapy for men without medical conditions who had low testosterone as a result of normal aging. But now, the FDA recommends that testosterone should be not used for low levels as a result of normal aging.

This FDA warning is based on older evidence that testosterone may increase the risk of heart attack and stroke, but newer research is challenging those thoughts. For example, a found that having low testosterone levels actually may be linked to heart problems.

Another recent study published in the journal The Aging Male, also found an association between low serum testosterone and heart problems. And although there needs to be more long-term studies done, on men who take testosterone has suggested that they do not have any increased risk of heart problems from the testosterone alone. In fact, found that testosterone supplementation may help some men avoid heart attacks.

The research suggests that the low testosterone itself may be linked to the heart problems, and not just the testosterone therapy. Thus, men who were taking testosterone were more prone to have heart attacks and strokes in the first place.

However, the FDA is still investigating what risks testosterone might have on men’s heart. They require that all medicine that contains testosterone is labeled with the possible increased risk of heart attack and stroke for men. They also encourage that men speak with their doctors about the benefits and risks before starting any testosterone therapy.

It’s also recommended that if you’re a male and are taking testosterone, you report any of the following conditions to your doctor and seek medical attention immediately, as they may be a sign of a heart attack:

  • chest pain
  • shortness of breath or trouble breathing
  • weakness in one part or one side of the body
  • slurred speech

An increased risk of sleep apnea is another aspect of testosterone therapy that affects cardiovascular health. With sleep apnea, you temporarily stop breathing many times while you sleep. Sleep apnea can raise your blood pressure, which increases your risk of stroke. It’s also associated with higher risk of heart valve disease and dangerous heart rhythms called arrhythmias.

Testosterone therapy may increase your cholesterol levels. Increased cholesterol buildup in the arteries supplying blood to your heart can lead to a heart attack. Other side effects include oily skin, fluid retention, and a decrease in the size of your testicles.

Receiving testosterone therapy may also affect your natural production of testosterone if your hormone levels are normal.

Hormone replacement is associated with certain side effects, but this therapy does help many men restore a diminished sex drive and build muscle mass. As people age, muscle mass tends to decline and your body tends to retain more fat.

Testosterone may help reverse those trends. However, if you’re going to take hormones, you should only do so under your doctor’s guidance.

Researchers continue to explore the risks and benefits of testosterone therapy. New research suggests that there may not be an increased risk for heart attacks and strokes with testosterone, but more studies are needed.

While testosterone may seem like a fountain of youth for many men, it may be right for some men but not right for others.

Have a comprehensive discussion with your doctor about what testosterone replacement therapy can and can’t do. Be sure to look at the possible side effects before you make a decision about testosterone therapy.