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Testosterone injections are injections of isolated testosterone. This hormone is present in both males and females, but the levels are naturally higher in males.

Testosterone therapy is becoming more common in the United States. Before recommending long-term testosterone therapy, doctors should make sure that the person understands and has weighed up the risks and benefits.

The following sections look at the uses of testosterone injections.

Treating low testosterone levels in males

Doctors may recommend testosterone injections to treat males with low testosterone levels. Low testosterone production by the testicles is called hypogonadism.

Low testosterone can have negative effects. The symptoms of low testosterone in males include a lower sperm count, a decrease in bone or muscle mass, increased body fat, and erectile dysfunction. Normal total testosterone levels in the bloodstream in healthy adult males are 280–1,100 nanograms per deciliter (ng/dl).

When treating hypogonadism, testosterone therapy can have the following benefits:

• improved sexual function
• increased lean muscle mass and strength
• improved mood
• better cognitive function
• possible reduction in osteoporosis

It is important to note that this therapy treats the symptoms of low testosterone rather than the underlying cause.

Anyone who suspects that they may have low testosterone can see a doctor for a diagnosis. However, the symptoms are quite general and could be due to other conditions or lifestyle factors.

Not all males with low testosterone will need treatment, and it is not always safe. The FDA have approved testosterone replacement therapy only for males with low testosterone due to disorders of the testicles, brain, or pituitary gland and not for natural age-related declines.

Read about other ways to increase testosterone levels and eight foods that may increase testosterone here.

Testosterone therapy in females

Testosterone therapy is more controversial in females than in males.

Normal total testosterone levels in healthy adult females are 15–70 ng/dl. Low testosterone in females can cause fertility problems, irregular periods, vaginal dryness, and a low sex drive. Despite this, doctors do not often recommend testosterone injections to treat low testosterone in females, as they can have masculinizing effects.

However, doctors may recommend testosterone therapy to help with hypoactive sexual desire disorder in females after menopause. Research has not supported their use for other signs and symptoms that people may experience after menopause, which include anxiety, mood changes, weight gain, and reduced bone density.

Currently, the FDA have not approved any products for testosterone therapy in females. Additionally, in the USA, there are no readily available formulations that provide the recommended treatment dose of 300 micrograms per day for females. As a result, a female will typically need a compounding pharmacy to fill the prescription.

Masculinizing hormone therapy

Testosterone therapy allows people to develop a more masculine appearance. Transgender men, nonbinary people, and other individuals may choose to use testosterone injections as part of a gender transition. This use of testosterone injections is known as masculinizing hormone therapy.

Testosterone therapy helps a person develop male sexual characteristics and reduce female characteristics, and it can lead to any of the following changes:

• changes in emotional and social functioning
• growing more facial hair
• increased body hair
• increased acne
• a deeper voice
• a receding hairline with male pattern baldness
• changes in the location of body fat
• increases in muscle mass
• absence of menstrual periods

These testosterone therapy regimens are similar to those that treat hypogonadism in males. Taking testosterone injections once a week may be the best way to keep the levels of this hormone even.

Testosterone injections can come in several varieties. These include:

• testosterone cypionate (Depo-Testosterone)
• testosterone enanthate (Xyosted and also available in its generic form)
• testosterone undecanoate (Aveed, which is a long acting formulation)

When a person receives a testosterone injection, the hormone directly enters the body through the muscle. People can choose between two methods:

• self-administering the injections at home, using a home injection kit to inject the hormone into the thigh
• having a doctor administer them into the buttocks muscle during a visit to the doctor's office

When having testosterone injections, people will usually visit their doctor every few months for monitoring. Treatments could last for a lifetime or be short-term, depending on the individual's circumstances.

Testosterone injections may be safe for many people when they follow a doctor's instructions. However, research has also linked testosterone therapy with several side effects and possible complications.

Possible negative effects of testosterone therapy may include:

• an increased risk of cardiovascular complications
• worsened symptoms in the lower urinary tract
• polycythemia, a rare type of blood cancer
• an increased risk of venous thrombosis

Some people may have an allergic reaction to testosterone injections. For example, testosterone undecanoate may cause a serious allergic reaction or breathing issues following the injection. Symptoms can include breathing problems, dizziness, and skin rashes.

Other forms of testosterone, including testosterone enanthate, may increase blood pressure, which can raise the risk of a stroke or heart attack.

People who have had strokes, heart attacks, heart disease, or high blood pressure should make the doctor aware of this before starting testosterone injections, as they may have a higher risk of complications.

If someone experiences any of the following symptoms after a testosterone injection, they should seek emergency medical attention:

• shortness of breath
• slow or difficult speech
• chest pain
• weakness or numbness in an arm or leg
• pain in the arms, neck, back, or jaw
• dizziness
• faintness

If a doctor prescribes male testosterone injections to an adolescent to treat a constitutional delay of growth and puberty, the goal will be to achieve an accelerated growth spurt during puberty. This therapy should not affect the final adult height that the adolescent reaches.

People may experience some mild side effects from testosterone injections, such as:

• breast enlargement or pain
• acne
• a deeper voice
• tiredness
• hoarseness
• back pain
• redness, bruising, pain, bleeding, or hardness at the injection site
• trouble sleeping or staying awake
• weight gain
• joint pain
• mood swings
• headaches

A person should speak to their doctor if they experience more serious side effects, such as:

• nausea or vomiting
• lower leg pain, redness, or warmth
• swelling of the hands, ankles, feet, or lower legs
• trouble breathing
• yellowing of the eyes or skin
• excessively long lasting erections
• changes in urination, such as difficulty urinating, increased frequency, weak flow, urinary urgency, or blood in the urine
• severe pain in the upper right part of the abdomen
• mood changes, including depression, anxiety, or feeling suicidal

Doctors may prescribe testosterone injections to treat low testosterone due to certain medical conditions in males. It does not cure the underlying condition, but it may help alleviate some of the symptoms. People can also use these injections to treat sexual dysfunction resulting from bodily changes after menopause or as part of masculinizing hormone therapy.

People should be aware of the possible serious complications of using testosterone in both the short-term and long-term. Doctors should do a thorough evaluation and, if testosterone replacement therapy is an option, discuss the benefit and risks with the person before prescribing it.

It is important to follow a doctor's instructions at all times to reduce any risks.