How much more muscle do steroids build?

Short answer

A lot. People who combined injections with strength training gained 6.1 kg of lean mass in 10 weeks, and users easily passed the drug-free ceiling. In exchange, heart attack risk was 3 times higher and death risk 4.6 times higher.

How much more muscle do steroids build?
'Drugs → explosive muscle' — what do the numbers say?
It's widely said that steroids (testosterone-type drugs) make muscle grow much faster. We checked the study numbers for how much more muscle they build and what they cost.
Muscle grew even without training
Bench up 9 kg in 10 weeks, placebo -1 kg
43 people were split into four groups and given testosterone injections or a placebo for 10 weeks. Comparing the non-training groups, the injection group added 9 kg to the bench press and 16 kg to the squat, versus -1 kg and 3 kg on placebo. Arm and thigh muscles grew only in the injection group.
Add training
1 kg of lean mass in 10 weeks
The group that got injections and lifted 3 times a week gained 6.1 kg of lean mass (muscle and everything except fat) in 10 weeks. The bench press rose 22 kg and the squat 38 kg, more than both non-training groups.
Higher doses, more growth
4 kg, 5.2 kg, 7.9 kg in 20 weeks
61 people got 5 different injection doses for 20 weeks; at the three highest, lean mass rose 3.4 kg, 5.2 kg and 7.9 kg. The higher the blood level, the bigger the thigh muscle volume and leg strength, and the lower the good cholesterol (HDL).
Past the drug-free limit
At 180 cm tall, 81 kg of lean mass is the ceiling
Measuring lean mass relative to height in 157 people, the 74 drug-free ones never went above 25. Many of the 83 users easily passed 25, and some passed 30. For someone 180 cm tall, that is 81 kg versus 97 kg of lean mass, a gap of about 16 kg.
Cost one: a weaker heart
The heart pumped out 52% vs 63%
Among 140 long-time lifters, the 86 who had used for more than 2 years had hearts that pumped out 52% of their blood per beat, versus 63% in the 54 non-users. The 58 current users were at 49%. They also had more plaque in the heart arteries, and the longer the use, the more it built up.
Cost two: heart disease and early death
3 times the heart attack risk
Following 1,189 people caught in drug testing for 11 years, heart attack risk was 3 times and irregular heartbeat 2.26 times that of 59,450 people from the general population. Of 62 people strongly suspected of drug use, 12.9% died within 12 years, versus 3.1% of the general population, a death risk 4.6 times higher.
Bottom line: big gains, paid for by the heart
1 kg in 10 weeks, at 3 times the heart attack risk
Steroids raised strength even without training, added 6.1 kg of lean mass in 10 weeks with training, and up to 7.9 kg in 20 weeks at higher doses. In exchange, the heart's pumping power dropped, heart attack risk was 3 times higher, and death risk 4.6 times higher.