Members of a group are more likely to lie after they inhale the "love hormone" oxytocin, a study has found.
This hormone is known to be released during close bonding between groups, and mothers also release it during childbirth and breastfeeding.
The results suggest that individuals in closely bonded groups are more likely to lie when it benefits the group than when it only benefits the individual.
The study is reported in PNAS journal.
When partaking in a financially rewarding task, groups given oxytocin nose spray lied significantly more than those doing the task alone. Those not given the hormone still occasionally lied, but a lot less.
Lead author Shaul Shalvi of Ben-Gurion University of the Negev, Israel, said his team was interested in how far people would go for their loved ones.
Dr Shalvi explained: "Do people do all they can to serve the group they belong to, even when it includes bending ethical rules such as lying?
"Our assumption is that our results support the functional approach to morality, where you decide what's right or wrong depending on the context of whether the act serves your loved ones, the group members.
"So participants inflated their outcomes in order to gain more money for their team."
In the task, participants inhaled oxytocin spray or a dummy spray and completed a computerised coin-flip task.
They were asked to predict whether the coin would land on heads or tails and only received a financial reward if they reported it correctly.
When completing the task in a group, each "correct" prediction earned the group money. Doing the task alone participants received the comparative same reward.
Crucially they had free reign to lie as the experimenter conducting the task could not see the results.
Some companies are now marketing oxytocin spray as an off-the-shelf "love hormone" but Dr Shalvi said his results suggested people "may want to be careful about pursuing such a route", as his results show that the hormone can also make people more dishonest.
But he added that the study once again highlights that lying is not necessarily always immoral.
"Our results indicate that people feel justified to bend ethical rules when their dishonesty serves people they care about," Dr Shalvi told BBC News.
Indeed there are countless examples of "flexible" honesty, such as when parents lie about their address to get their children into a good school.
Another prominent example that irate England football fans may remember, Diego Maradona's 1986 "hand of god" goal which helped Argentina secure a 2-1 victory against England.
Much to the dismay of his opposition, Maradonna later admitted that he knew it was a hand ball. He remains unrepentant.
Commenting on the research, Thomas Baumgartner from the University of Basel, Switzerland, said: "The study is interesting and well-conducted and provides further evidence about the complex role oxytocin might play in modulating social decision-making and behaviour."