For decades, Nigerians have paid for their leaders and former rulers to get medical treatment overseas. That courtesy also extends to senior government employees.
This is despite taxpayers' funding of the State House Medical Center, said to be Nigeria's best-equipped facility, which serves the president and vice president, their families and staff. The center's budget this year of 3.8 billion naira to care for fewer than 1 000 people represents 1 percent of the entire public health budget for the country's 170 million people.
"For years, billions have been budgeted for the State House Medical Centre while it has always been evident that every president mostly accessed medical facilities outside the country, going back to the 1980s," said Oluseun Onigbinde, co-founder of BudgIT, an organisation that tries to bring clarity to the West African nation's opaque budget.
The mysterious nature of Buhari's absence is adding to the unhappiness at home, as one of Africa's largest economies and oil producers lurches through a recession.
His government has not said what exactly his health issues might be or when he will return. The president's trip, originally scheduled from January 20 to February 6, was described as a vacation during which he would undergo routine medical tests. It has been extended for further tests.
Officials insist that Buhari is "hale and hearty", and he was well enough this week to speak by telephone with US President Donald Trump.
Human rights lawyer Femi Falana said Nigerians should seize on the president's medical leave to demand adequate funding for public hospitals he described as "mortuaries for the masses."
"The practice of allowing poor citizens to die of preventable diseases while top public officers and rich private citizens are allowed to travel abroad for medical treatment can no longer be justified," he said in a lecture this week, noting that Nigerians have a life expectancy of 52 years.
It is not clear how much the country's taxpayers pay for leaders' treatments abroad.
Former first lady Patience Jonathan has claimed that half of $31.5m frozen in a corruption investigation was a government payout for medical bills she incurred in London in 2013. Ever-witty Nigerians took to social media to ask if she was buying eternal life.
High yearly allowances
The Ministry of Health estimated that Nigeria paid about $1bn for government officials traveling abroad for medical care in 2014, with ordinary Nigerians spending about $6.3bn in 2015 for what is called medical tourism.
Senior Nigerian officials get "high yearly allowances" for health care abroad which "provides them opportunity to demand amounts to take care of their non-health care needs like shopping abroad," economist Vitalis Chi. Nwaneri wrote in his 2013 book "Governing the Ungovernable."
Former military dictator Gen. Ibrahim Babangida returned home this month from a six-week "medical vacation" in Switzerland. Last year, he was treated for weeks in Germany.
Taxpayers also footed the bill when former President Umaru Yar'Adua received months of medical treatment in Saudi Arabia in 2008-2009, before he returned home to die in office.
In April, Buhari announced that his government would no longer pay for officials to travel abroad for medical services available at home. But two months later, the president was in London for treatment of an ear infection.
"The best-funded clinic in Nigeria does not suffice to treat the president's ear infection. Nor does the president have enough confidence in the same clinic to do his 'routine checkups' there," novelist Okey Ndibe wrote at saharareporters.com.
Private health care
"Imagine, then, the fate of Nigerians who have no choice but must seek treatment at the ill-equipped, wretchedly funded hospitals in our country?" he asked.
Nigeria has just five hospital beds and not even one doctor for every 100 000 people, as opposed to an average of 35 beds and 24 doctors per 100 000 in South Africa, which has the continent's most advanced medical care, according to a PricewaterhouseCoopers study in 2015.
Nigerians who can afford it shun even private health care at home.
Because the country has one of the world's worst infant and maternal mortality rates, women fly to the United States and Britain to have babies safely delivered. The risk of a woman dying because of pregnancy or childbirth in Nigeria is one in 15, compared to one in 5 000 in developed nations, according to Dr Chris Akani, professor of obstetrics and gynecology at Nigeria's College of Health Sciences at the University of Port Harcourt.
Buhari's medical bills do not come with bed at a heftily priced five-star hotel, as did those of predecessors. The 74-year-old anti-corruption crusader known for his simple lifestyle is staying at the residence of the Nigerian High Commission in London, a spokesman said.