Supplements marketed as testosterone boosters often contain herbs, vitamins, or minerals like zinc and vitamin D. Correcting a genuine deficiency in zinc or vitamin D may help if you are deficient, but in men who are not deficient, most of these products show little or no proven benefit on testosterone levels or symptoms.
There are real concerns too. The supplement industry is loosely regulated in many regions, so contents can be inconsistent, mislabelled, or contaminated, and some products have been found to contain undeclared pharmaceutical ingredients or anabolic steroids that can harm the liver, heart, and fertility.
If you have symptoms of low testosterone, the right step is a proper assessment rather than self-treatment. See a doctor for blood tests and to look for treatable causes such as poor sleep, obesity, or thyroid issues. Genuine low testosterone is treated with prescribed, monitored therapy, not over-the-counter boosters.