What is natural bodybuilding?

In one line

Natural bodybuilding is bodybuilding in which competitors are drug tested, so that only people who have not used muscle-building drugs compete against each other.

What is natural bodybuilding?
What does 'natural' in a show's name mean?
Some bodybuilding shows have the word 'natural' in their name or on their posters. In everyday English it means 'as found in nature'. In bodybuilding, the word has a more specific meaning.
In short
Bodybuilding with drug testing
Natural bodybuilding is bodybuilding in which competitors (people who enter the show) are drug tested, so that only people who have not used muscle-building drugs compete against each other. That is why it is also called 'drug-tested' bodybuilding. It means competing with a body built by training and eating.
Why it began
Pushing back against a drug-normal culture
In bodybuilding, using muscle-building drugs came to be treated as normal. Drug-free bodybuilding grew from the 1970s as a response. The first professional show held by the natural organization WNBF, in 1990, allowed only competitors who had passed drug tests onto the stage.
Background: hormones
Testosterone builds male body features
A hormone is a substance made in the body that travels in the blood and sends signals to other organs. Testosterone is the main hormone that builds male body features such as facial hair, a deep voice and muscle. Women's bodies have it too, but in much smaller amounts.
Banned drugs 1
'Steroids' are modeled on testosterone
Anabolic steroids are man-made drugs modeled on testosterone. 'Anabolic' refers to the effect of making muscle grow. These muscle-building drugs are the main drugs natural shows ban, and the NPC, WNBF and OCB all ban them.
Banned drugs 2
The banned list is long
Natural organizations keep long lists of banned drugs. Besides steroids, the lists include growth hormone and 'diuretics', drugs that increase urine to remove water from the body. Checking whether a medicine or supplement contains a banned ingredient is the competitor's responsibility.
Test 1: urine test
Testing the urine of top finishers
The most basic check is a urine test. A competitor's urine is collected and a lab looks for traces of banned drugs. At natural shows of the US professional body IFBB Pro League, 1st and 2nd place in each division are tested backstage. The WNBF and OCB also test without warning when there is no show.
Test 2: lie detector
Measuring the body's reactions to questions
A lie detector is a machine that tries to spot lies by measuring changes in breathing rate, blood pressure and the skin's electrical response while a person answers questions. At the WNBF, every competitor must pass this test before going on stage. Pro qualifier shows of the US amateur body NPC, and the OCB, also run a similar test before the show.
Same divisions
'Natural' is a type of show, not a division
'Natural' is not the name of a division. Natural shows hold the same divisions, such as bodybuilding, classic physique, men's physique, bikini and figure. The difference is that these shows run drug tests.
If a test is failed
Suspension, or even a lifetime ban
At the NPC, a first failure means 1 year out of competition, a second means 2 years, and a third means a lifetime ban. At the WNBF, a positive result for steroids or growth hormone means a lifetime ban on the first failure. Refusing a test also leads to disqualification.
A common misconception
Is it only for people who never used drugs?
No. The NPC, OCB and WNBF set their rules as 'years since last use', not 'never in a lifetime'. For muscle-building drugs, the period is 3 years for NPC natural shows, 7 years for the OCB and 10 years for the WNBF. Someone who used drugs in the past (unless banned for life after a failed test) becomes eligible after that period if they pass testing.
Summary
A stage for drug-tested competitors
Natural bodybuilding is bodybuilding that drug-tests competitors so that only people who have not used muscle-building drugs compete. The condition is not 'never in a lifetime' but no drug use for the period each organization sets. Related terms: anabolic steroids, diuretics, bodybuilding division.