A consumer magazine has revealed that home health kits could be a waste of time, effort and money.
Which? said that DIY kits for problems such as prostate cancer and stomach ulcers can cause false alarms or provide fake reassurance for worried individuals.
Chief Executive Peter Vicary-Smith said: "Self-test health kits could be a useful tool, but the lack of clear information about how to use them could do more harm than good.
"As your GP may well have to carry out their own tests to confirm a positive diagnosis anyway, you may be better off saving your money and going straight to your GP."
Experts from the group examined six kits, available online or at chemists for between £4.99 and £15.99, and interviewed 64 members of the public about their use.
But the results were described as "hit and miss" as some consumers revealed that prostate test results led to them not seeking medical help.
The research also found gaps in information which could lead to unnecessary worry.
For example, a Boots blood glucose test kit marketed as helping "in the early detection of diabetes" failed to mention that glucose levels can be raised after a meal, Which? said.
And a Boots bowel test kit did not provide dietary advice such as avoiding red meat for three days before the test.
There were also examples of "baffling language, with consumers in one case asked to draw blood from the "hillside" of the finger.
Other potentially confusing terms included "separation membranes", "desiccant" and "in-vitro diagnostic device".
The Selfcheck Health Test, which tests for an antigen (PSA) linked to prostate problems, did not explain that recent sexual activity, a urine infection or vigorous exercise, could raise PSA levels, the researchers said.
And the Simplicity Stomach Ulcer Screening Test was misleadingly named, Which? also said.