Testosterone is dangerous, and not recommended.

Edit: Read this before you misunderstand what I’m saying. All I am asking is for medication to be treated with respect. It is not going to cause the apocalypse, but neither is it sensible to be using unless it is needed.

Do not play with it. Do not test its patience.

My gender specialist told me before supplying me with it that he estimates that it will take ~5 years off my life. He told me that it is dangerous, and he could not recommend it.
He takes it himself. The point is, for both him and me, it’s a necessity. It’s an aggressive drug, but there’s no choice about it.

I am going to copy out the list of side-effects on my leaflet:
Common side effects (between 1 and 10 people in every 100)
TESTOGEL may cause headaches, hair loss, development of painful, tender or enlarged breasts, changes to your prostate gland, diarrhoea, dizziness, an increase in blood pressure, changes to your mood, changes in laboratory blood test results (increase in the number of red blood cells in the blood, lipids), skin hypersensitivity, stinging and loss of memory.
Other side effects have been observed during treatment with oral or injectable testosterone: weight gain, changes of the salt in the blood, muscular pain, nervousness, depression, hostility, breathing problems during sleep, yellowing of the skin (jaundice), changes in the results of tests that check how the liver is working, seborrhoea, sex drive changes, reduction in the number of sperm, frequent or prolonged erections, blockages that may make it difficult to pass urine, water retention, hypersensitivity reactions.

'Changes in laboratory blood test results' may not sound like a problem, but you tell me that it's not when your increased red blood cell count causes you to get a blood clot, which is potentially fatal. You tell me that it's not when your increased lipids causes you to have a stroke or heart attack.

Testosterone could be your undoing. Some people on this site will die, when they would have survived had they not been on testosterone. It will kill some of us.

Scared? I bloody hope so. It is not a toy.

People who are truly transsexual should respond to it with “I don’t like this, it’s unfair you’ve got me scared over something I have no choice about. I would be dead without it, anyway.”

If you even have an inkling that this is something you can consider not taking, then pause. You need to pause, and think about whether this is worth possibly dying over. Would 5 years of maleness in return for 70 years of femaleness be a reasonable trade? A transman would say emphatically yes. 70 years of femaleness would be an impossibility. 

Finally, to actual transmen. Do not despair. Just make sure to have a healthy enough diet and amount of exercise, and keep up with your blood tests. You will probably be unaffected if you take precautions, but risk will still remain.
Enjoy the life you’ve got. Who cares if it increases the risk of this, that, and the other, because it gives us another chance at life. We are living on time that we’d never naturally have. Thank science, and make the most of it. It makes no difference if testosterone giveth and taketh away, because we start with nothing.