Meisam, an Iranian-American doctor, is growing increasingly concerned about her elderly grandmother in Iran, who has leukaemia.

“As a physician who treats patients like this daily in the United States I feel guilty that I am helpless to take care of a loved family member back home,” she said.

“She has been unable to get ahold of her chemotherapy drugs. None of the pharmacies are carrying it or have a supply more than a few days or a few weeks.”

Trump says he would meet with Iran's leaders without preconditions

Meisam’s family, with the help of her grandmother’s oncologist, are searching for new suppliers who may be able to import the medicines, but as US sanctions start to bite, they don’t know what will be possible.

“Sanctions hurt ordinary people on the streets and do not inflict pain at all whatsoever on the government,” Meisam added.

“How is withholding chemotherapy from my 80-year-old grandmother helpful to anyone’s objective?”

In the past few weeks, international companies have begun to pull out of Iran after threats from US President Donald Trump that businesses must choose between trade with Tehran or trade with the US.

The first round of "snapback" US sanctions came into effect at the beginning of August after Mr Trump followed through on a campaign trail promise to pull out of the Iran nuclear deal. A new round is due in November.

Iran protests – in pictures Show all 11 1 /11 Iran protests – in pictures Iran protests – in pictures University students at an anti-government protest inside Tehran University, 30 December 2017 AP Iran protests – in pictures A university student at a protest inside Tehran University while a smoke grenade is thrown by anti-riot Iranian police, 30 December 2017 AP Iran protests – in pictures University students at a protest inside Tehran University, 30 December 2017 AP Iran protests – in pictures University students run away from the police during an anti-government protest inside Tehran University, 30 December 2017 AP Iran protests – in pictures An image grab taken from a handout video released by Iran's Mehr News agency reportedly shows a group of men pulling at a fence in a street in Tehran, 30 December 2017 AFP/Getty Iran protests – in pictures Demonstrators gather to protest in Tehran, 30 December 2017 AP Iran protests – in pictures Iranians chant slogans as they march in support of the government near the Imam Khomeini grand mosque in Tehran, 30 December 2017 AFP/Getty Iran protests – in pictures Iranians chant slogans as they march in support of the government near the Imam Khomeini grand mosque in Tehran, December 30 2017 Iran protests – in pictures Iranian clerics take part during a state-organized rally against anti-government protests in the country, in the holy city of Qom, south west Iran, 3 January 2018 EPA Iran protests – in pictures In this photo provided by the Iranian Students' News Agency, a clergyman takes a picture of a pro-government demonstration in the southwestern city of Ahvaz, Iran, 3 January 2018 ISNA via AP Iran protests – in pictures Pro-government demonstrators gather at the Massoumeh shrine in Iran's holy city of Qom, some 130 kilometres south of Tehran, 3 January 2018 AFP/Getty

The landmark Barack Obama-era legislation lifted crippling sanctions on the Iranian economy in return for curbs on Iran’s nuclear programme.

Just a few weeks in, more than 80 million ordinary Iranians are starting to feel the pinch caused by the new sanctions, the National Iranian American Council (NIAC) said.

The “devastating” impact of sanctions amounts to “collective punishment” of Iranian citizens, NIAC president Jamal Abdi said in a statement.

“The grievous harm sanctions cause the Iranian people cannot be overstated: As the economy and unemployment levels make daily life unbearable for millions of Iranians, families are choked off from life-saving medicines and starved of critical infrastructure,” he said.

“These sanctions will threaten Iran’s compliance with the nuclear accord, while also undercutting hopes for Iranian moderation, harming the Iranian middle class and empowering Iranian hardliners and extremists.”

While the UK, France, Germany, China and Russia – the other signatories of the 2015 nuclear deal – have all agreed to abide by the terms of the agreement, the Trump administration has yet to set out in full its hardline policy on Iran.

In the interim, for ordinary Iranians, the brief hope that followed the implementation of the nuclear accord has evaporated and many are now fearful for the future.

The Iranian government can no longer purchase US bank notes, which has sent the already fragile rial tumbling, exacerbated Iran’s housing affordability crisis and caused food prices to rocket. A travel ban imposed last year has cut off millions of diaspora families.

Imported medicines are increasingly hard to come by; jobs in Iran’s graphite, coal and metal processing industries are on the line; and air travel has become more expensive and difficult as international carriers phase out flights. On Thursday, British Airways announced its London-Tehran flight, popular with dual nationality families and adventurous tourists over the last few years, would end in September.

White House: Trump will not allow Iran to keep making threats against US

The Iranian currency has already lost half of its value since April this year, leading to street protests in several Iranian cities over the cost of living and government corruption.

Speaking from Israel on Thursday, John Bolton, the US national security adviser, said the reimposition of sanctions has already proven more successful than expected.

“Let me be clear, the reimposition of the sanctions, we think, is already having a significant effect on Iran's economy and on, really, popular opinion inside Iran,” he told Reuters.

Iranian officials have taken a defiant stance to the Trump administration’s move: the head of the powerful Revolutionary Guards said the sanctions amount to “psychological warfare”.

Despite the souring of relations, however, many analysts do not see the renewed Washington-Tehran hostilities escalating.

“On the Iranian side, the mindset from both more pragmatist and hardline politicians is that the Trump administration is so unpredictable it may be better to wait out his term and hope he doesn’t get re-elected, rather than rise to any bait,” Dr Sanam Vakil, an associate fellow at Chatham House in London, previously told The Independent.

For Iranian families, however, Mr Trump’s tenure is already changing lives for the worse.

Mary, a US citizen who left Iran in 1981, said she still has nightmares of the old travel sanctions, which meant she never got the chance to see her father in person before he died.

Iran's 'Trumpism' contest Show all 10 1 /10 Iran's 'Trumpism' contest Iran's 'Trumpism' contest A picture taken on July 3, 2017 shows a cartoon of US President Donald J. Trump and First Lady Melania Trump on display at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranian cartoonist Hadi Asadi poses for a picture with a trophy and an award next to cartoons of US President Donald J. Trump, at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranians look at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranian reformist cleric Mahmoud Doaei looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian man looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest An Iranian woman looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images Iran's 'Trumpism' contest Iranian reformist cleric Mahmoud Doaei looks at cartoons of US President Donald J. Trump at an exhibition of the Islamic Republic's 2017 International Trumpism cartoon and caricature contest, in the capital Tehran on July 3, 2017. / AFP PHOTO / ATTA KENARE (Photo credit should read ATTA KENARE/AFP/Getty Images) AFP/Getty Images

She works two jobs to help support her sister in Iran, who has a brain-damaged son.

Mary is adamant that US sanctions prevented her nephew from receiving better care after a car accident, and is bracing herself for the impact of new sanctions on his treatment.

“I am furious with all that's going on and scared for the Iranian people,” she said.