As our professional advisors here at Drug Testing Kits UK, advise: "If an employee fails a saliva or urine drug test, the employer must follow their drug & alcohol policy & the consequences of the failure. This may include disciplinary action such as suspension or termination of employment. However, each case should be looked at individually according to the circumstances. For example, in some cases, the employee may have taken a form of legal medication that could have affected the results" 
Did You Know?
According to the drug-screening company Quest Diagnostics, the number of workers who tested positive for illegal drug use, reached a 14-year high in 2018, & marijuana topped the list of most commonly detected illegal substances" 
A Step-By-Step Guide to Standard Procedure
As our Drug Testing Kits UK's health science advisor notes: in the first instance, once a positive result has shown up on the multi drug testing kit, the employee should be advised of such. - This way, they have an opportunity to see the result for themselves. They may ask to have the drug test re-taken right away, which you should accommodate. Important note: obviously allowing the test to be done again on another day, would allow time for the drug/s to clear their system, so to that end, the request should be denied. Drug Testing Kit UK approved multi-panel drug tests offer a long shelf life, and as bulk orders save your company/organisation money, it is a good idea to always keep a supply in stock for times like these 
Always abide by your health and safety/drug policy when deliberating as to whether, or under what circumstances, you will engage in a conversation with an applicant or member of staff, about the results; and what the consequence of their illicit drug abuse will amount to, for example: termination of employment, or suspension (while a laboratory analyses a second test) 
As any positive result could be due to the employee taking prescription drugs, and even medically prescribed cannabis, it is very important that you have a form (already drawn up), which they can voluntarily fill in. This should be entitled: 'Prescription Drug Use.' They can then list any prescribed medications, including cannabis; how often they take it/them; and the full details (name and address, etc.), of the doctor who prescribed it, and whether this doctor is their normal GP. And very importantly, at the bottom of the page, it should state: "I have given this information voluntarily." And they should sign and date it. With regard to employee privacy rights and The Data Protection Act: "If an employer gathers information about the prescribed medication taken by staff, the Data Protection Act applies. In other words, the right of workers to a measure of privacy has legal support. This support is not absolute, however. The Data Protection Act allows employers a certain degree of freedom. This means that employers can request health data, but must do so only if they satisfy one of the Act’s “sensitive data conditions. That is to say, if: the collection of the heath information is necessary to maintain health and safety, or the collection is needed to prevent discrimination against disabled workers, or every member of staff has agreed to the collection" . So in this instance, the first condition would apply
Always be prepared for the employee arguing that their drug test is incorrect. For example: they could say that they were travelling to work with someone who smoked cannabis in the car (with the windows shut), and could not avoid all the second-hand smoke; or they may say that they went to a party and had some dubious brownie cakes
Be sure that your company/organisation, always has a stock of top quality, highly accurate, instant result saliva multi drug testing kits and urine multi drug testing kits on the premises. (They have a long shelf life, and the packaging is designed to take up very little space). One reason for this, is that if a positive result is detected on an on-site Drug Testing Kit UK's saliva or urine test, then in order to legally confirm this result, a urine sample must be sent by courier to a UK registered laboratory for confirmation drug testing using GCMS (Gas chromatography–mass spectrometry). This an analytical procedure which combines the features of gas-chromatography and mass spectrometry in order to determine different substances within a drug test sample. Note: this should be done, even if the Drug Testing Kit UK's instant test was a urine test, a saliva test, or a fingerprint test. In due course, the drug testing laboratory will send you a written report. (This will be needed if an accident has occurred in the workplace; or outside the workplace - if the employee is representing the company/organisation. And will be essential if the matter goes to an industrial tribunal, or if legal action is going to be pursued against the employee later down the line).
"In some companies, failing a drug test results in instant dismissal, particularly in safety-critical job roles. Having said that, a positive result does not always lead to this, particularly if there is no clear evidence that the drugs were consumed at work. Additionally, the results of instant testing must also be confirmed by laboratory testing, & normally employees are suspended whilst this investigation takes place 
Ensuring That Your Employees' Welfare is Taken into Account
"It is important to be mindful that: "an employer’s duty to their employee extends to the employee’s welfare, including their mental health & well-being. If their potential drug or alcohol misuse is a result of long-term stress, the issue can become a medical matter rather than a disciplinary one. This also means that it is possible to retain the member of staff in the future (subject to them taking reasonable time off to recover and seek specialist support" , the latter of which should be proved to the employer in writing by the drug rehabilitation provider/specialist (with as much ongoing detail as possible).
. Allan, L. (2023). "Everything you need to know about Workplace Drug Testing." CPD College.
. SHRM (2020). "What to Do When an Employee Fails a Drug Test."
. Watson. K. (2021). "Can Employer Demand to See Prescribed Medication Details?"