Drug testing: Kissing under the Mistletoe at Christmas

Lolita Tsanaclis

Lolita Tsanaclis

on Dec 19, 2022

Drug testing: Kissing under the Mistletoe and other Christmas activities

At Cansford we often get asked questions through our live chat regarding the more subtle nuances of drug and alcohol testing. We were asked this week whether a person could test positive after kissing a Cocaine user, which with Christmas fast approaching got us thinking about mistletoe, Christmas parties and New Year celebrations and scenarios around whether the answer could be a positive yes or no.

Things to consider

The first things to take into consideration is that the results depend on factors such as metabolism, purity of a substance, how often the drug was taken, how quickly the hair grows on the person being tested, what chemicals have been used, the time period being tested etc. The dose transferred by a kiss is so minuscule that a hair test is unlikely to be positive. However, if an oral fluid test is taken shortly after, it might be positive…so could prove to be an unlucky kiss!!!

How often a drug is taken

It is popularly believed that hair analysis can give an indication of the level of drug use – but perhaps in this case, an ‘in the moment’ test would be better to detect use. A hair strand test would determine a longer period of time and whether an individual could be graded as a heavy user or a light user.

However, this could be considered as a dangerous over-simplification. There are many factors affecting levels of drugs and metabolites in hair. For example, differences in metabolism, dose, purity and frequency of drug consumed should be taken into consideration as well as colour of hair and the effect of cosmetic hair treatment.

Chemicals used

If we were to test and collect a sample from festive partygoers, any use of glitter, festive hair dye or hairsprays, gels, mousses, or any treatments could potentially affect the test result. Anything that damages the outer layers of hair, such as bleaches and dyes may reduce levels of drug in hair.

Hair growth

Hair typically grows at about one centimetre per month. When tested, each centimetre of hair therefore reflects one month’s history of drug use (or non-use). This is why hair strand testing is able to provide such a large window of detection, assessing drug use as far back as six months, depending on the hair length.

Cheating a test

But that’s not to say we can’t take a test if you’ve spray-painted or changed your hair with chemicals, gels and or dyes. We can still take hair from the chest, underarm, legs and pubic area. Alternatively, we can clip a nail sample from a fingernail or toenail to test as well. In body hair or nails, the window of detection is different from head hair because of the biology of those matrices.

Time period

The hair strand testing method can be used to detect virtually all drug and alcohol use markers, starting at seven days after use, depending on the hair length. 

Test results also indicate the month in which a donor ingested a substance and can therefore be used to build a ‘picture’ of substance use over time. Hair takes around seven days to grow out of the scalp – which is the minimum time window a hair test can detect. It may therefore be necessary to use hair testing in conjunction with blood and (oral fluid) saliva testing.

For example, if you attend a Christmas party on December 24th, 2022, then a reasonable timescale for a sample collection from a donor could possibly be in the New Year 2023 but that absolutely depends on how fast or slow your hair grows. If the hair growth is slow then this collection date may be a bit later in the month or the start of the next one.

Not everyone is the same, and an individual’s hair growth rate can be different compared to someone else’s – where the hair growth rate may vary from 0.75 to 1.5 cm/month. 

Purity of a substance

If we revert to the original question about Cocaine, we know it can come in several different forms – including tablets, powder, or crystals, so the purer the substance, the higher the result may be and the longer that it can remain in someone’s system.


The answer as to whether a person can test positive for kissing a Cocaine user is extremely negligible. Due to the nature of individual circumstances, while we can’t say it’s impossible, it could be extremely improbable.

In 2016, the Sport Dispute Resolution Centre of Canada (SDRCC) determined a pole vaulter had inadvertently absorbed cocaine while kissing a woman he'd met the night before the national competition, after undergoing a urine test, which detected the drug.

"There's a minimum amount you need to be exposed to," said Dr. David Juurlink, head of clinical pharmacology and toxicology at Sunnybrook Health Sciences Centre in Toronto, in a story published at the time. "It's very difficult to imagine a scenario in which the exchange of saliva through kissing transfers from one person to another a sufficient amount of cocaine to result in a positive test."

Therefore, we would conclude the same would apply regarding Cocaine use and kissing under the mistletoe this Christmas or New Year.

If you have any questions about this blog or wish to know more about our drug and alcohol testing please do get in touch. We are here through our live chat, by email through or by phone on (0)29 2054 0567 .


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Lolita Tsanaclis

Lolita Tsanaclis

Dr. Lolita Tsanaclis, Chief Scientific Officer of Cansford Laboratories Limited, has been developing methods for the analysis of drugs in hair since 1993. She has been involved in drug testing using hair, blood and oral fluid samples for medico-legal and workplace sectors for over three decades. Dr Tsanaclis is published extensively as author and as co-author in highly regarded peer-reviewed publications and scientific presentations.

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