It may be some time before the results of a trial are known.
Some large trials can involve thousands of people and it can take years before each one has been assessed and the results have been collected and analysed.
Even when this has happened, there is a further period, usually of several months, when the research is looked at and commented on by other scientists (called a peer review) as a check on its quality.
At the end of the trial, the researcher should make the results available to anyone who took part and has said they want to know the results.
If researchers do not offer you the results, and you want to know, ask for them.
All the main public funders of health research and the larger medical research charities require researchers to place a copy of their research on UK PubMed Central when it is published. It is a condition of funding.
Continue to next section: Why all research should be registered